Water purification type pervious concrete with pH sensing function and preparation method of water purification type pervious concrete

Abstract

The invention discloses water purification type pervious concrete with pH induction and a preparation method of the water purification type pervious concrete, and belongs to the technical field of pervious concrete. The water purification type pervious concrete is prepared from the following raw materials: geopolymer slurry, aggregate and a chitosan capsule coated with a phosphate core material, wherein the mass ratio of the geopolymer slurry to the aggregate is (0.35-0.5): 1; the geopolymer slurry comprises a silicon-aluminum material, an alkali activator and water, and the water-cement ratio is 0.40-0.5; the modulus of the alkali activator is 0.5-2, and the alkali equivalent is 5-20%; the mass ratio of the aggregate to the chitosan capsule is (3-17): 1; the phosphate core material comprises phosphate and a porous framework carrier material. The obtained pervious concrete has good adsorption performance, can rapidly capture heavy metals in a discontinuous acid environment to form precipitates, can exert an excellent water purification function in practical application, and has wide application prospects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of pervious concrete, and particularly relates to a water purification type pervious concrete with pH response and a preparation method thereof. BACKGROUND

[0002] Groundwater is an important source of drinking water, and humans have widely and continuously relied on groundwater in history. However, with the development of industry, a large number of mineral resources exploitation and industrial pollution, heavy metal pollution in groundwater has become a serious problem. Heavy metals have persistence, non-degradability, high toxicity, and are easy to accumulate in animals, plants and human bodies, endangering human health.

[0003] In order to solve the heavy metal pollution and improve the quality of groundwater, there are currently a variety of treatment technologies. Permeable reactive barrier (PRB) is an in-situ treatment technology for repairing groundwater pollution, through which the contaminated water can react with the reaction medium to convert into less polluted compounds or be fixed on the reaction material. Pervious concrete is formed by bonding single or discontinuous graded coarse aggregate and paste, and has many pores in the structure, which can pass a large amount of solution, and has certain strength, and can be used as PRB material. The adsorption capacity of pervious concrete for heavy metals is derived from the paste and aggregate. The geopolymer replaces the cement paste as the paste of the pervious concrete, and the geopolymer has a network structure and certain alkalinity, and has certain heavy metal adsorption capacity. At the same time, the aggregate of the pervious concrete can be modified to enhance its adsorption capacity. However, the adsorption capacity of the geopolymer-based pervious concrete for heavy metals will be greatly weakened in an acidic environment, and the adsorption capacity will be greatly reduced at pH 5-6, the water purification effect is poor, and it cannot be applied to an acidic environment, and is greatly limited in practical application. Although phosphate has the potential to adsorb heavy metal ions in an aqueous solution in an acidic to weakly neutral range, it is difficult to control the release content of phosphate directly released in the environment, and a large amount of phosphate will be wasted and secondary pollution will be caused to the environment in the face of intermittent heavy metal release environment. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a water purification type pervious concrete with pH response and a preparation method thereof, which has good adsorption performance and can quickly capture heavy metals to form a precipitate in an intermittent acidic environment, and can play an excellent water purification function in practical application.

[0005] In order to solve the above technical problems, the following technical solutions are adopted in the present application: A water purification type pervious concrete with pH response is provided, and the raw materials include a geopolymer paste, an aggregate and a chitosan capsule wrapped with a phosphate core material. The mass ratio of the geopolymer paste to the aggregate is 0.35-0.5:1; The geopolymer paste comprises a silico-aluminate material and an alkali activator, and the water-cement ratio is 0.40-0.5; the modulus n(SiO2) / n(R2O) of the alkali activator is 0.3-2, and the alkali equivalent is 5-20%; The mass ratio of the aggregate to the chitosan capsule is 3-17:1; The phosphate core material comprises a phosphate and a porous framework carrier material.

[0006] The water-cement ratio is the mass ratio of water to the silico-aluminate material, and the amount of water includes water in the alkali activator and additional water; the modulus of the alkali activator is the relative molar ratio of silicon dioxide (SiO2) to alkali metal oxide (R2O, i.e. Na2O or K2O); and the alkali equivalent is the mass percentage of alkali metal oxide in the alkali activator to the silico-aluminate material.

[0007] According to the above scheme, the silico-aluminate material is one or a combination of any number of fly ash, metakaolin, slag, coal gangue, steel slag, etc.

[0008] According to the above scheme, the alkali activator is a mixed solution of sodium hydroxide and sodium silicate, or a mixed solution of potassium hydroxide and potassium silicate.

[0009] According to the above scheme, the aggregate is construction gravel or pebbles. Preferably, the aggregate has a particle size of 4.75-16 mm and a single grading.

[0010] According to the above scheme, the mass ratio of the phosphate to the framework carrier material is 0.2-0.9:1.

[0011] According to the above scheme, the chitosan capsule with the phosphate core material has a particle size of 4.75-9.5 mm.

[0012] According to the above scheme, the phosphate core material has a particle size of 1.18-2.36 mm.

[0013] According to the above scheme, the phosphate is one or a mixture of any number of sodium dihydrogen phosphate, diammonium phosphate, and potassium dihydrogen phosphate.

[0014] According to the above scheme, the framework carrier powder is one or a combination of any number of fly ash, metakaolin, bentonite, and rice husk ash.

[0015] According to the above scheme, the phosphate core material is prepared by uniformly mixing a phosphate solution with a framework carrier powder to form a mass having a particle size range of 1.18-2.36 mm, and then drying to obtain.

[0016] Preferably, the mass-volume ratio of the phosphate and water in the phosphate solution is 0.5-1.5 g:1 ml.

[0017] Preferably, the mass ratio of the phosphate and the skeleton carrier powder is 0.2-0.9:1.

[0018] Preferably, the drying conditions are: drying treatment at 40-50℃ for 20-30h.

[0019] According to the above scheme, the preparation of the chitosan capsule with a phosphate core material is carried out by the following steps: 1) gradually adding the phosphate core material into the acetic acid solution of chitosan, and mixing thoroughly; 2) dropping the mixture obtained in step 1) into the alcohol-alkali solution drop by drop, and standing to obtain the capsule; 3) washing the capsule obtained in step 2), and then placing it in a crosslinking agent solution, standing, and then taking it out, washing and drying to obtain the chitosan capsule with a phosphate core material.

[0020] Preferably, in step 1), the chitosan is any one or any mixture of carboxymethyl chitosan, hydroxypropyl chitosan, tetracaine hydrochloride chitosan, N-trimethyl chitosan, and N-maleated chitosan.

[0021] Preferably, in step 1), the preparation of the acetic acid solution of chitosan includes: mixing chitosan with 4-6% (v / v) acetic acid solution at a ratio of 1 g:20-100 ml, stirring for 6-8h until the chitosan is completely dissolved, and standing for use.

[0022] Preferably, in step 1), the mass ratio of the phosphate core material and the acetic acid solution of chitosan is 1:1.5-10.

[0023] Preferably, in step 2), the standing time is 30-60min.

[0024] Preferably, in step 2), the standing is until the capsule with a particle size range of 4.75-9.5mm is formed.

[0025] Preferably, in step 2), the alcohol-alkali solution includes an alcohol solution and an alkali solution at a volume ratio of 1.5-4:1; wherein the alcohol solution is one or more of ethanol and methanol, and the volume fraction is 60-80%; and the alkali solution is one of sodium hydroxide solution and potassium hydroxide solution, and the concentration is 1-2 mol / L.

[0026] Preferably, in step 3), the crosslinking agent is one or more of glutaraldehyde, genipin, and sodium tripolyphosphate.

[0027] Preferably, in the step 3), the concentration of the crosslinking agent solution is 0.1-5% (v / v); preferably, the volume ratio of the crosslinking agent solution to the capsule is 2-5:1.

[0028] Preferably, in the step 3), the standing time is 10-60 min.

[0029] Preferably, in the step 3), the drying temperature is 30-60 DEG C.

[0030] According to the above scheme, the water purification type water permeable concrete is capable of dissolving chitosan and releasing phosphate in an environment with pH < 6.

[0031] The application provides a preparation method of the water purification type water permeable concrete, comprising the following steps: The silico-aluminate material is mixed with an alkali activator to prepare a geopolymer slurry, aggregate and chitosan capsules wrapped with a phosphate core material are added into the geopolymer slurry, and then the mixture is stirred uniformly, and then is left to stand and cured to obtain the water purification type water permeable concrete with pH response.

[0032] According to the above scheme, the standing time is 1-2 days; and the curing time is 6-7 days.

[0033] The application provides a water purification type water permeable concrete with pH response, which comprises a geopolymer slurry, aggregate and chitosan capsules wrapped with a phosphate core material. In the application, the phosphate and the porous carrier skeleton material are used together as the phosphate core material, on one hand, the porous structure is convenient for temporarily storing the phosphate and avoiding the early loss of the phosphate; on the other hand, the carrier skeleton material can play a supporting role and is easy to form a group and be wrapped by chitosan.

[0034] The water permeable concrete is put into an intermittent sewage underground water environment as a permeable reaction barrier, can adsorb heavy metals through the geopolymer slurry in a normal state, when encountering acid rain and sewage environment, the pH of the underground water is reduced, the chitosan is dissolved due to the acid-soluble property, the phosphate in the chitosan is released to quickly capture the heavy metals in the solution to form more stable precipitates, and the chitosan itself as a common adsorbent still has more functional groups such as amino groups and hydroxyl groups, and can participate in the adsorption reaction to enhance the adsorption and adsorption capacity of the water permeable concrete.

[0035] Compared with the prior art, the application has the following beneficial effects: 1.The present application provides a kind of pH sensitive water purification pervious concrete, to be wrapped with the shell of phosphate core material Cystosepiment capsule as part of aggregate, when encountering acidic pollution environment, the characteristic of Cystosepiment acid solution makes it dissolve and release phosphate, quickly adsorbs and captures heavy metal, forms stable precipitate, improves the adsorption performance of pervious concrete in acidic environment, is conducive to the protection of environment, while Cystosepiment itself has more functional groups, can further enhance the adsorption efficiency of pervious concrete;The pervious concrete obtained by the present application has good adsorption performance, and can quickly capture heavy metal to form precipitate in intermittent acidic environment, and can play excellent water purification function in practical application, and has wide application prospect.

[0036] 2.Further, the present application prepares phosphate core material into clusters by mixing phosphate into porous carrier skeleton material in advance;Then, by using the characteristic of Cystosepiment that is easy to dissolve in acidic environment, phosphate is mixed into Cystosepiment in dissolved state, and then Cystosepiment is coagulated by alkali-alcohol solution, to obtain Cystosepiment capsule wrapped with phosphate, and the strength of capsule is increased by crosslinking treatment, so that it can be mixed into pervious concrete for use, which not only can play the role of aggregate, but also can realize excellent adsorption effect of pervious concrete in acidic environment.

[0037] 3.The present application provides a kind of preparation method of pH sensitive water purification pervious concrete, which is simple to operate, simple in working procedure, low in raw material cost, and can be well applied in actual production. DETAILED DESCRIPTION

[0038] The technical solutions of the present application will be described in detail below combined with specific embodiments, but the described embodiments are only part of the embodiments of the present application, and all other embodiments obtained by those skilled in the art without creative labor based on the embodiments in the present application belong to the protection scope of the present application.

[0039] Example 1 A kind of preparation method of pH responsive water purification pervious concrete is provided, including the following steps: 1) preparation of phosphate core material Take sodium phosphate 15g, deionized water 10ml, and stir for 1h using a magnetic stirrer. Then add 25g fly ash, mix uniformly, and prepare clusters with particle size of 1.18-2.36mm, and place them in a 50℃ oven for 24h, take out, and obtain phosphate core material, for standby use.

[0040] 2) preparation of Cystosepiment capsule wrapped with phosphate core material Take 5 g of carboxymethyl chitosan, put it into 100 ml of 5% acetic acid solution (v / v), and stir it with a magnetic stirrer for 8 h to make it fully dissolved. Then add the phosphate core material obtained in step 1), mix well, and obtain a chitosan-phosphate mixture.

[0041] Take 300 ml of 75% ethanol and 200 ml of 1 mol / L NaOH to obtain an alcohol-base solution. Drop the chitosan-phosphate mixture obtained into it to form capsules with a particle size range of 4.75-9.5 mm. Let it stand for 50 min, filter it out, rinse it with deionized water, and then place it in a 2.5% volume concentration glutaraldehyde solution for 30 min. Then take it out, rinse it with deionized water, and dry it in a 40°C oven for 24 h to obtain chitosan capsules coated with phosphate core material, which is ready for use.

[0042] 3) Preparation of water permeable concrete Take 81.28 g of SP38 type water glass (Na2SiO3 content is 35.5%), add 109.2 g of water and 40.5 g of NaOH to prepare an alkali activator, take 383.3 g of slag, mix it with the alkali activator, and then add 1555 g of crushed stone and 100 g of the phosphate chitosan capsules obtained in step 2), mix well, pour the concrete into a 100 mm x 100 mm x 100 mm cubic mold, let it stand for 1 d, take it out, and continue to cure it in a standard curing box for 6 d to obtain a pH-sensitive water purification type water permeable concrete.

[0043] Example 2 A method for preparing a pH-responsive water purification type water permeable concrete is provided, which comprises the following steps: 1) Preparation of phosphate core material Take 15 g of potassium dihydrogen phosphate and 50 ml of deionized water, and stir it with a magnetic stirrer for 1 h. Then add 26 g of fly ash, mix well, and prepare a mass with a particle size range of 1.18-2.36 mm. Dry it in a 50°C oven for 24 h to obtain the phosphate core material, which is ready for use.

[0044] 2) Preparation of chitosan capsules coated with phosphate core material Take 6 g of carboxymethyl chitosan, put it into 150 ml of 5% acetic acid solution (v / v), and stir it with a magnetic stirrer for 8 h to make it fully dissolved. Then add the phosphate core material obtained in step 1), mix well, and obtain a chitosan-phosphate mixture.

[0045] Take 400 ml 75% ethanol and 200 ml 1 mol / L NaOH mixture to get alcohol-alkali solution, drop the obtained chitosan-phosphate mixture into it, form capsules with particle size range of 4.75-9.5 mm, stand for 50 min, filter out, rinse with deionized water, then place in 2.5% volume concentration glutaraldehyde solution for 30 min, take out, rinse with deionized water, dry in 40°C oven for 24 h, get chitosan capsules with phosphate core material, ready for use.

[0046] 3) Preparation of pervious concrete Take SP38 type water glass (Na2SiO3 content is 35.5%) 85.5 g, add 114.9 g water and 42.6 g NaOH to prepare alkali activator, take 403.8 g of slag, mix with alkali activator, then add 1405 g of crushed stone, mix well with 250 g of phosphate chitosan capsules obtained in step 2), pour the concrete into a 100 mm x 100 mm x 100 mm cubic test mold, stand for 1 d, then demold and take out, continue to cure in a standard curing box for 6 d to obtain a pH-sensitive water purification pervious concrete.

[0047] Example 3 A method for preparing a pH-responsive water purification pervious concrete is provided, comprising the following steps: 1) Preparation of phosphate core material Take 25 g of sodium dihydrogen phosphate and 50 ml of deionized water, stir for 1 h with a magnetic stirrer. Then add 84 g of fly ash, mix uniformly, and then place in a 50°C oven to dry for 24 h to obtain phosphate core material, ready for use.

[0048] 2) Preparation of chitosan capsules with phosphate core material Take 10 g of carboxymethyl chitosan and put it into 200 ml of 5% acetic acid solution (v / v), stir for 8 h with a magnetic stirrer to dissolve it completely, then add the phosphate core material obtained in step 1), mix well to obtain a chitosan-phosphate mixture.

[0049] Take 500 ml 75% ethanol and 250 ml 1 mol / L NaOH to get alcohol-alkali solution, drop the obtained chitosan-phosphate mixture into it, form capsules with particle size range of 4.75-9.5 mm, stand for 50 min, filter out, rinse with deionized water, then place in 2.5% volume concentration glutaraldehyde solution for 30 min, take out, rinse with deionized water, dry in 40°C oven for 24 h, get chitosan capsules with phosphate core material, ready for use.

[0050] 3) Preparation of pervious concrete Take SP38 type water glass (Na2SiO3 content of 35.5%) 81.28g, add 109.2g water and 40.5g NaOH to configure alkali activator, take slag 383.3g, add alkali activator to mix well, then add 1555g of crushed stone, 100g of pure chitosan capsules, mix well, pour the concrete into a 100mmx100mmx100mm cubic test mold, take it out after 1d of standing, continue to maintain in a standard curing box for 6d to obtain a geopolymer pervious concrete mixed with chitosan capsules.

[0051] Comparative Example 1 Take SP38 type water glass (Na2SiO3 content of 35.5%) 81.28g, add 109.2g water and 40.5g NaOH to configure alkali activator, take slag 383.3g, add alkali activator to mix well, then add 1555g of crushed stone, 100g of pure chitosan capsules, mix well, pour the concrete into a 100mmx100mmx100mm cubic test mold, take it out after 1d of standing, continue to maintain in a standard curing box for 6d to obtain a geopolymer pervious concrete mixed with chitosan capsules.

[0052] Comparative Example 2 Take 5g of chitosan and put it into 100ml of acetic acid solution (5%), use a magnetic stirrer to stir for 8h to make it fully dissolved. Take 300ml of 75% ethanol and mix with 200ml of 1mol / L NaOH, drop the chitosan solution into it to form capsules with a particle size range of 4.75-9.5mm, stand for 50min, filter and take out, rinse with deionized water, then place in glutaraldehyde solution and stand for 30min, take out, rinse with deionized water, and place in a 40℃ oven to dry for 24h to obtain pure chitosan capsules, ready for use.

[0053] Take SP38 type water glass (Na2SiO3 content of 35.5%) 81.28g, add 109.2g water and 40.5g NaOH to configure alkali activator, take slag 383.3g, add alkali activator to mix well, then add 1555g of crushed stone, 100g of pure chitosan capsules, mix well, pour the concrete into a 100mmx100mmx100mm cubic test mold, take it out after 1d of standing, continue to maintain in a standard curing box for 6d to obtain a geopolymer pervious concrete mixed with chitosan capsules.

[0054] The water permeability and mechanical properties of the samples of Examples 1-3 and Comparative Examples 1-2 were tested, and the results are shown in Table 1, which meet the performance requirements of pervious concrete.

[0055] Table 1 Water permeability coefficient and 28d compressive strength of pervious concrete

[0056] The water permeable concrete samples prepared in Examples 1-3 and Comparative Examples 1-2 were respectively placed in Pb 2+ Static adsorption tests were conducted with 500 mg / L of Pb(OH)2, and initial adsorption environments of neutral (pH = 7) and acidic (pH = 3) were set. The Pb 2+ concentrations were detected to determine the Pb 2+ removal rates, and thus the water purification effects. The experimental results of the examples and comparative examples are shown in Table 2: Table 2 24h static removal rates of water permeable concrete on Pb 2+

[0057] It should be understood that, for those of ordinary skill in the art, improvements or changes can be made according to the above description, and all such improvements and changes shall fall within the protection scope of the appended claims of the present application.​

Claims

1. A pH-responsive permeable concrete for water purification, characterized in that, The raw materials include geopolymer slurry, aggregates, and chitosan capsules encapsulating a phosphate core material; wherein: The mass ratio of the geopolymer slurry to the aggregate is 0.35-0.5:1; The geopolymer slurry comprises aluminosilicate material and an alkali activator, with a water-cement ratio of 0.40-0.5; the alkali activator has a modulus of 0.3-2 and an alkali equivalent of 5-20%. The mass ratio of the aggregate to the chitosan capsule is 3-17:1; The phosphate core material comprises phosphate and a porous framework carrier material.

2. The permeable concrete with clean water properties according to claim 1, characterized in that, The silicoaluminate material is one or any combination of fly ash, metakaolin, slag, coal gangue, and steel slag; the alkali activator is a mixed solution of sodium hydroxide and sodium silicate, or a mixed solution of potassium hydroxide and potassium silicate; the aggregate is crushed stone or pebbles for construction.

3. The permeable concrete for water purification according to claim 1, characterized in that, The mass ratio of phosphate to porous framework carrier material is 0.2-0.9:

1.

4. The permeable concrete for water purification according to claim 1, characterized in that, The chitosan capsules containing the phosphate core material have a particle size of 4.75-9.5 mm; the phosphate core material has a particle size of 1.18-2.36 mm.

5. The permeable concrete for water purification according to claim 1, characterized in that, Chitosan is one or any combination of carboxymethyl chitosan, hydroxypropyl chitosan, tetracaine hydrochloride chitosan, N-trimethyl chitosan, and N-maleyl chitosan; the phosphate is one or any combination of sodium dihydrogen phosphate, ammonium dihydrogen phosphate, and potassium dihydrogen phosphate; the skeleton carrier powder is one or any combination of fly ash, metakaolin, bentonite, and rice husk ash.

6. The permeable concrete for water purification according to claim 1, characterized in that, The phosphate core material is prepared by uniformly mixing a phosphate solution with a skeleton carrier powder to form clumps with a particle size range of 1.18-2.36 mm, followed by drying.

7. The permeable concrete for water purification according to claim 1, characterized in that, The chitosan capsules encapsulating the phosphate core material are prepared through the following steps: 1) Add the phosphate core material to the acetic acid solution of chitosan and mix thoroughly; 2) The mixture obtained in step 1) is added dropwise to an alcohol-alkali solution and allowed to stand to obtain capsules; 3) After washing the capsules obtained in step 2), place them in a cross-linking agent solution, let them stand, then take them out, wash them, and dry them to obtain chitosan capsules encapsulating phosphate core material.

8. The permeable concrete for water purification according to claim 7, characterized in that, In step 1), the acetic acid solution of chitosan is prepared by mixing chitosan with a 4-6% acetic acid solution, wherein the mass-volume ratio of chitosan to the 4-6% acetic acid solution is 1g:20-100ml; the mass ratio of phosphate core material to chitosan acetic acid solution is 1:1.5-10. In step 2), the alcohol-alkali solution comprises an alcohol solution and an alkali solution with a volume ratio of 1.5-4:1; wherein the alcohol solution is one or more of ethanol and methanol, with a volume fraction of 60-80%; and the alkali solution is one of sodium hydroxide solution and potassium hydroxide solution, with a concentration of 1-2 mol / L. In step 3), the concentration of the crosslinking agent solution is 0.1-5%, and the volume ratio with the capsule is 2-5:1; the crosslinking agent is one or more of glutaraldehyde, genipin, and sodium tripolyphosphate.

9. The permeable concrete for water purification according to claim 7, characterized in that, In step 2), the settling time is 30-60 minutes; in step 3), the settling time is 10-60 minutes.

10. A method for preparing permeable concrete of the water purification type according to any one of claims 1-9, characterized in that, Includes the following steps: Geopolymer slurry is prepared by mixing silica-alumina material with an alkali activator. Aggregate and chitosan capsules containing phosphate core material are added to the geopolymer slurry. After stirring evenly, the mixture is allowed to stand and be cured to obtain a water-purifying permeable concrete with pH response.

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